The broad utilization of methods of radioactive indication in scientific research and by industries for monitoring various continuous analytical and production processes has put forward strict requirements concerning instruments for measuring the radioactivity of continuous liquid flows. The demand for such instruments has been increased by the development of such industries as nuclear power generation and radio-chemistry.
The hitherto known apparatus for continuous measurement of the radioactivity of solutions of matters, however, offer inadequately accurate response and are operable exclusively with relatively low flow rates of the solutions being monitored, which impairs the realization of the advantages offered by radioisotope-type detection of substances.
Improving the response and enhancing the dynamic characteristics of apparatus and arrangements for continuously measuring the radioactivity of solutions of matters is a prerequisite for substantially increasing the accuracy and speeding up the rate of continuous methods of analysis, e.g. liquid chromatography methods, and thus for speeding up the action and perfecting the response of monitoring systems of radiochemical production processes and nuclear power stations. An improvement of such arrangements will ultimately lead to fuller utilization of the methods of continuous analysis, offering as the latter are considerable advantages over intermittent processes, such as smaller labor consumption, economy of materials, on-time control of the process, minimum environment pollution, better working conditions, etc.
Known in the art is an arrangement for continuously measuring the radioactivity of solutions of matters in a homogeneous mixture with a liquid scintillator, comprising a system of conduits interconnecting a multi-channel pump, a mixing device for mixing a solution of a matter with a liquid scintillator, and a measuring chamber (see Journal of Chromatography, 1972, Vol. 72, No. 2, pp. 307-308).
In this arrangement the measuring chamber is a helix made of a tube constructed of polytetrafluoroethylene (such as that designated by the trademark Teflon). A probe mixture produced by blending homogeneously the water solution of a matter with a liquid scintillator is supplied from the mixing device into the chamber, and then from the latter into a drain receptacle.
To provide for adequately effective measurement of radioactivity and for obtaining a homogeneous probe mixture, there is used a scintillator containing toluene and Triton X-100, a trademark for polyethylene glycol alkyl aryl ether, in a 1:1 ratio, in case of which the maximum permissible value of water-to-scintillator ratio by volume is 1:3, while the volume of the measuring chamber, to ensure conditions of minimum agitation of the solution passing through the chamber, is 1.2 ml.
In a majority of cases this volume is insufficient to ensure high response and to attain statistically dependable outcome of measurements at high solution flow rates, even with aid of a costley scintillator containing Triton X-100. Should the volume of the chamber in the known construction be increased, either by increasing the diameter of the Teflon tube, or by increasing its length, the poor hydrodynamic properties of the apparatus would result in substantial stirring or agitation of the solution being analyzed, on account of turbulence. This becomes particularly apparent at high flow rates, which, in cases when the radioactivity of solutions of matters obtained at the outcome of a chromatography column is measured, considerably impairs the chromatograph.
It is an object of the present invention to provide an arrangement which would offer a high response at continous measurement of the radioactivity of solutions of matters.
It is another object of the present invention to improve the hydrodynamic characteristics of the arrangement.
It is still another object of the present invention to enhance the economy of the arrangement.